Asymmetric stent apparatus and method

ABSTRACT

A stent-graft system comprising a graft member and a stent having a connection end interconnected with the graft member and a free end opposed thereto. The stent includes a plurality of struts extending between the connection end and the free end and at least two of the struts having different lengths such that the free end has a nonuniform profile. A method of securing at least one end of a stent-graft within a vessel is also provided.

RELATED PATENT APPLICATION

This patent application is a continuation and claims the benefit of U.S.patent application Ser. No. 11/861,828, filed Sep. 26, 2007, namingMichael V. Chobotov as inventor, entitled ASYMMETRIC STENT APPARATUS ANDMETHOD, and having attorney docket no. TRI-0656-UT, which isincorporated by reference herein in its entirety, including all text anddrawings.

BACKGROUND OF THE INVENTION

The present invention relates to a system for the treatment of disordersof the vasculature. More specifically, the invention relates to a systemfor the treatment of disease or injury that potentially compromises theintegrity of a flow conduit in the body. For example, an embodiment ofthe invention is useful in treating indications in the digestive andreproductive systems as well as indications in the cardiovascularsystem, including thoracic and abdominal aortic aneurysms, arterialdissections (such as those caused by traumatic injury), etc. thatinclude a curved lumen.

Medical devices for placement in a human or other animal body are wellknown in the art. One class of medical devices comprises endoluminaldevices such as stents, stent-grafts, filters, coils, occlusion baskets,valves, and the like. A stent typically is an elongated device used tosupport an intraluminal wall. In the case of a stenosis, for example, astent provides an unobstructed conduit through a body lumen in the areaof the stenosis. Such a stent may also have a prosthetic graft layer offabric or covering lining the inside and/or outside thereof. A coveredstent is commonly referred to in the art as an intraluminal prosthesis,an endoluminal or endovascular graft (EVG), a stent-graft, or endograft.

An endograft may be used, for example, to treat a vascular aneurysm byremoving or reducing the pressure on a weakened part of an artery so asto reduce the risk of rupture. Typically, an endograft is implanted in ablood vessel at the site of a stenosis or aneurysm endoluminally, i.e.by so-called “minimally invasive techniques” in which the endograft,typically restrained in a radially compressed configuration by a sheath,crocheted or knit web, catheter or other means, is delivered by anendograft delivery system or “introducer” to the site where it isrequired. The introducer may enter the vessel or lumen from an accesslocation outside the body, such as purcutaneously through the patient'sskin, or by a “cut down” technique in which the entry vessel or lumen isexposed by minor surgical means. The term “proximal” as used hereinrefers to portions of the endograft, stent or delivery system relativelycloser to the end outside of the body, whereas the term “distal” is usedto refer to portions relatively closer to the end inside the body.

After the introducer is advanced into the body lumen to the endograftdeployment location, the introducer is manipulated to cause theendograft to be deployed from its constrained configuration, whereuponthe stent is expanded to a predetermined diameter at the deploymentlocation, and the introducer is withdrawn. Stent expansion typically iseffected by spring elasticity, balloon expansion, and/or by theself-expansion of a thermally or stress-induced return of a memorymaterial to a pre-conditioned expanded configuration.

Among the many applications for endografts is that of deployment inlumen for repair of an aneurysm, such as a thorasic aortic aneurysm(TAA) or an abdominal aortic aneurysm (AAA). An AAA is an area ofincreased aortic diameter that generally extends from just below therenal arteries to the aortic bifurcation and a TAA most often occurs inthe descending thoracic aorta. AAA and TAA generally result fromdeterioration of the arterial wall, causing a decrease in the structuraland elastic properties of the artery. In addition to a loss ofelasticity, this deterioration also causes a slow and continuousdilation of the lumen.

The standard surgical repair of AAA or TAA is an extensive and invasiveprocedure typically requiring a week long hospital stay and an extendedrecovery period. To avoid the complications of the surgical procedure,practitioners commonly resort to a minimally invasive procedure using anendoluminal endograft to reinforce the weakened vessel wall, asmentioned above. At the site of the aneurysm, the practitioner deploysthe endograft, anchoring it above and below the aneurysm to relativelyhealthy tissue. The anchored endograft diverts blood flow away from theweakened arterial wall, minimizing the exposure of the aneurysm to highpressure.

Intraluminal stents for repairing a damaged or diseased artery or to beused in conjunction with a graft for delivery to an area of a body lumenthat has been weakened by disease or damaged, such as an aneurysm of thethorasic or abdominal aorta, are well established in the art of medicalscience.

While intraluminal stents are advantageous in anchoring the device, animproved system for aligning stents in curved vessels or lumens isdesired.

SUMMARY OF THE INVENTION

In one aspect, the invention provides a stent-graft system comprising agraft member and a stent having a connection end interconnected with thegraft member and a free end opposed thereto. The stent includes aplurality of struts extending between the connection end and the freeend and at least two of the struts having different lengths such thatthe free end has a nonuniform profile.

In another aspect, the invention provides a method of securing at leastone end of a graft within a vessel. The method comprises: positioningwithin the vessel a stent-graft comprising a stent and a graft with aconnection end of the stent connected to an end of the graft, the stenthaving a free end opposite the connection end, the stent including aplurality of nonuniform struts such that the free end has at least oneshort strut and at least one long strut; positioning the stent-graftwithin the vessel such that the at least one short strut is aligned withan inner radial curvature of the vessel; and deploying the stent.

Other aspects and advantages of the present invention will be apparentfrom the detailed description of the invention provided hereinafter.

The invention is best understood from the following detailed descriptionwhen read in connection with the accompanying drawings. It is emphasizedthat, according to common practice, the various features of the drawingsare not to scale. On the contrary, the dimensions of the variousfeatures are arbitrarily expanded or reduced for clarity. Included inthe drawings are the following figures:

FIG. 1 shows a prior art endovascular graft portion fully deployedwithin an angulated internal vasculature of the patient.

FIG. 2 shows an endovascular graft portion in accordance with anembodiment of the present invention fully deployed within an angulatedinternal vasculature of the patient.

FIG. 3 shows a flat pattern of an embodiment of a stent in accordancewith an embodiment of the present invention.

FIG. 4 shows a flat pattern of another alternative embodiment of a stentin accordance with the present invention.

FIG. 5 shows a portion of an endovascular graft according to anembodiment of the present invention partially deployed within anangulated internal vasculature of the patient.

FIG. 6 shows the endovascular graft portion of FIG. 5 fully deployedwithin the internal vasculature of the patient.

DETAILED DESCRIPTION OF THE INVENTION

Although the invention is illustrated and described herein withreference to specific embodiments, the invention is not intended to belimited to the details shown. Rather, various modifications may be madein the details within the scope and range of equivalents of the claimsand without departing from the invention.

Unless otherwise stated, the term “graft” or “endovascular graft” isused herein to refer to a prosthesis capable of repairing and/orreplacing diseased vessels or portions thereof, including generallytubular and bifurcated devices and any components attached or integralthereto. For purposes of illustration, the graft embodiments describedherein may be used in the endovascular treatment of abdominal aorticaneurysms (AAA) or thoracic aortic aneurysms, however, otherapplications are within the scope of the present invention. For thepurposes of this application, with reference to endovascular graftdevices, the term “proximal” describes the end of the graft that will beoriented towards the oncoming flow of bodily fluid, typically blood,when the device is deployed within a body passageway. The term “distal”therefore describes the graft end opposite the proximal end. Finally,while the drawings in the various figures are accurate representationsof the various embodiments of the present invention, the proportions ofthe various components thereof are not necessarily shown to exact scalewithin and among or between any given figure(s).

Referring to FIG. 1, a prior art stent graft 110 is illustrated deployedwithin an angulated vessel 1 of a patient. The stent graft 110 includesa stent 140 connected to a graft 113 as is known in the art. The stent140 includes a plurality of struts 141 which each have a uniform lengthto define a uniform free end 142 with all of the struts 141 terminatingin a common plane P. With such a stent 140 positioned in an angulatedvessel 1, the stent 140 may not align properly. For example, an innerstrut 141 a may liftoft from an inner radial curvature 3 of the vessel 1as indicated at arrow A. Alternatively, an outer strut 141 b maypenetrate the vessel wall at an outer radial curvature 5 of the vessel1.

Referring to FIGS. 2 and 3, a stent graft 10 in accordance with a firstembodiment of the invention will be described. An end of the graft 10 isillustrated and may represent the proximal or distal end of the graft10. The graft 10 includes a generally tubular structure or graft bodysection 13 comprised of one or more layers of fusible material, such asexpanded polytetrafluoroethylene (ePTFE). An inflatable cuff 16 isdisposed at or near the end 14 of graft body section 13. A neck portion23 is disposed in the vicinity of graft body section end 14 and servesas an additional means to help seal the deployed graft against theinside of a body passageway. Graft body section 13 forms a longitudinallumen 22 configured to confine a flow of fluid therethrough.

An attachment ring 24 is affixed to or integrally formed in graft bodysection 13, or as shown in FIG. 2, at or near graft body section end 14and neck portion 23. In the embodiment of FIG. 1, attachment ring 24 isa serpentine ring structure comprising apices 28. Other embodiments ofattachment ring 24 may take different configurations. Attachment ring 24may be made from any suitable material that permits expansion from aconstrained state, most usefully a shape memory alloy havingsuperelastic properties such as nickel titanium (NiTi). Other suitableattachment ring 24 materials include stainless steel, nickel-cobaltalloys such as MP35N, tantalum and its alloys, polymeric materials,composites, and the like. Attachment ring 24 (as well as all stents andattachment rings described herein) may be configured to self-expand fromthe illustrated radially constrained state.

Some apices 28 may also comprise a attachment ring connector element(not shown). The number of connector elements may vary and can bedistributed, for example, on every apex, every third or fourth apex, orany other pattern are within the scope of the present invention.

Graft 10 further comprises one or more stents 40 having, in the deployedstate, a generally free end 42 and a connection end 44. FIG. 2illustrates a proximal stent 40, but the stents 40 may additionally oralternatively be provided on the distal end of the graft 10. In the caseof a bifurcated graft, a stent 40 may be provided on the distal end ofeach leg of the bifurcated graft.

As shown in FIG. 2, stent 40 is typically, though not necessarily, madea part of graft 10 by having the connection end 44 affixed or connectedto attachment ring 24 via connector elements as described in detailbelow. The connection end 44 of stent 40 may also be affixed or embeddeddirectly to or in neck portion 23 and/or other portions of graft bodysection 13. In addition, the attachment ring and the stent may not bemechanically or otherwise fastened to one another but rather unified,formed of a monolithic piece of material, such as NiTi.

This configuration of stent 40, attachment ring 24, neck portion 23, andcuff 16 helps to separate the sealing function of cuff 16, whichrequires conformation and apposition to the vessel wall within whichgraft 10 is deployed without excessive radial force, from the anchoringfunction of stent 40 (attachment ring 24 and neck portion 23 playintermediate roles).

Referring to FIGS. 2 and 3, each stent 40 of the present inventiongenerally comprises a series of interconnected struts 41 which will bedescribed in more detail hereinafter. Each stent 40 further comprisesstent connector elements 48 at the connection end 44 thereof. The stentconnector elements 48 are configured to be affixed or otherwiseconnected to attachment ring connector elements 30 via coupling members(not shown), for example, threads or wires. The stents 40 may bemanufactured from any suitable material, including the materialssuitable for attachment ring 24. When manufactured from a shape memoryalloy having superelastic properties such as NiTi, the stents 40 may beconfigured to self-expand upon release from the contracted state. Thestrut structure is often formed as a flat structure, as illustrated inFIGS. 3-4, and thereafter, wrapped and connected in a cylindrical orother configuration, as illustrated in FIG. 2.

Each stent 40 may include one or more barbs 43. A barb 43 can be anyoutwardly directed protuberance, typically terminating in a sharp pointthat is capable of at least partially penetrating a body passageway inwhich graft 10 is deployed (typically the initial and medial layers of ablood vessel such as the abdominal aorta). The number of barbs, thelength of each barb, each barb angle, and the barb orientation may varyfrom barb to barb within a single stent 40 or between multiple stents 40within a single graft. Although the various barbs 43 may be attached toor fixed on the stent struts 41, it is preferred that they be integrallyformed as part of the stent struts 41, as shown in the various figures.

As illustrated, the struts 41 can have various configurations andlengths. In the present invention, the struts 41 have differing lengthssuch that the stent 40 has a nonuniform free end 42. That is, the endsof all different struts 41 do not lie along a single plane. In thepresent embodiment, the short struts 41 a define the distal mostportions of the free end 42 while the long struts 41 c define theproximal most portions of the free end 42 and the intermediate struts 41b define portions therebetween. In the present embodiment, the free end42 has a sinusoidal configuration as illustrated in FIG. 3. For someembodiments, the strut lengths slope to a pair of short struts offsetapproximately ninety degrees relative to the long struts. For someembodiments, the short struts are configured to be aligned with an innerradial curvature and outer radial curvature of an angulated vessel.

Referring to FIG. 2, in a preferred deployment, the stent 40 ispreferably aligned within an angulated vessel such that a pair of theshort struts 41 a are positioned against an inner radial curvature 3 ofthe vessel 1 and a second pair of the short struts 41 a are positionedagainst an outer radial curvature 5 of the vessel 1. To facilitatealignment, one or more of the struts 41 may be provided with aradiopaque marker 50 or the like. In this orientation, the long struts41 c are along the sides of the vessel 1 and do not cause liftoff orpenetration.

Referring to FIGS. 4-6, a second embodiment of the invention isillustrated. The stent graft 10′ is similar to in the previousembodiment, but the stent 70 includes a portion which is generally thesame as the stent 40 of the previous embodiment and a secondary stentportion 80 connected thereto. The secondary stent portion 80 has aplurality of struts 81 which have a uniform length such that thesecondary stent 80 has a generally uniform free end 82, i.e. each of thestruts 81 terminating in generally the same plane P. The connection end84 is desirably connected to the long struts 41 c of the stent portion40.

In use, the stent 70 is preferably deployed in a multistage manner. Thestent 70 is positioned within the vessel 1 with the secondary stentportion 80 aligned with a generally straight portion 7 of the vessel 1and deployed. The secondary stent portion 80 may connect to the straightportion 7 of the vessel 1, for example, via barbs or the like, andanchor the stent graft 10′ in position. Since the vessel portion 7 isstraight, the uniform struts 81 are not subject to liftoff orpenetration. At this time, the nonuniform stent portion 40 remains in aconstrained state via belt 35 or the like.

The staged deployment of the stent 70 also facilitates self-alignment ofthe stent portion 40 and graft 10. Upon deployment of the secondarystent portion 80, the graft 13 is free to expand and distal fluid flowflows into the graft 13 and creates a “windsock” effect. That is, thedistal fluid flow applies a slight distal force upon the graft 13. Thisdistal force helps to align the graft 13 and the stent 40 within thevessel 1, which is particularly advantageous during deployment of thestent graft within the angulated vessel 1, for example, which is anaortic arch.

The stent portion 40 may thereafter be deployed by release of the belt35 whereby the stent portion 40 deploys in a manner similar to describedabove. As shown in FIG. 6, the stent 40 is preferably aligned within theangulated vessel 1 such that a pair of the short struts 41 a arepositioned against the inner radial curvature 3 of the vessel 1 and asecond pair of the short struts 41 a are positioned against the outerradial curvature 5 of the vessel 1. Again, to facilitate orientation,one or more of the struts 41 may be provided with a radiopaque marker 50or the like. Orientation is preferably performed prior to deployment ofthe secondary stent portion 80. As in the previous embodiment, in thisorientation, the long struts 41 c are along the sides of the vessel 1and do not cause liftoff or penetration.

While preferred embodiments of the invention have been shown anddescribed herein, it will be understood that such embodiments areprovided by way of example only. Numerous variations, changes andsubstitutions will occur to those skilled in the art without departingfrom the spirit of the invention. Accordingly, it is intended that theappended claims cover all such variations as fall within the spirit andscope of the invention.

What is claimed is:
 1. A stent-graft system comprising: a tubular graftmember comprising at least one longitudinal lumen configured to confinea flow of fluid therethrough; and a cylindrical stent including: aconnection end interconnected with the tubular graft member, a free endaxially opposed to the connection end, a plurality of struts extendingbetween the connection end and the free end, a first pair of adjacentshort struts diametrically opposed to a second pair of adjacent shortstruts, the short struts defining a distal most portion of the free end,and a first pair of adjacent long struts diametrically opposed to asecond pair of adjacent long struts, the long struts defining a proximalmost portion of the free end with the pairs of long struts beingcircumferentially offset approximately ninety degrees relative to thepairs of short struts.
 2. The stent-graft system according to claim 1wherein each of the struts circumferentially disposed between the firstpair and second pair of adjacent long struts is shorter than the firstpair and second pair of adjacent long struts.
 3. The stent-graft systemaccording to claim 2 wherein the strut lengths of the strutscircumferentially disposed between the first pair and second pair oflong struts decrease towards the adjacent first pair and second pair ofshort struts.
 4. The stent-graft system according to claim 1 wherein thestruts define a sinusoidal profile at the free end of the stent.
 5. Thestent-graft system according to claim 1 wherein the cylindrical stentfurther comprises one or more barbs which are configured to extend fromthe stent struts.
 6. The stent-graft system according to claim 1 furthercomprising a secondary stent which is connected to the free end of thefirst pair and second pair of adjacent of long struts.
 7. Thestent-graft system according to claim 6 wherein the secondary stent hasa uniform profile at a free end thereof.
 8. The stent-graft systemaccording to claim 1 wherein a marker is provided on at least one of thestruts to identify an orientation of the stent within a vessel.
 9. Thestent-graft system according to claim 1 further comprising at least onebelt which is releasably secured about the stent between the connectionend and the free end and which is releasable therefrom.
 10. Thestent-graft system according to claim 1 wherein the stent connection endfurther comprises a plurality of connection elements configured forattachment to corresponding connection members on the tubular graftmember.